The epithelial cells of the mammalian colon play a vital role in water and electrolyte reabsorption. These cells are polarized, with an absorptive mucosal surface exposed to the contents of the gastrointestinal tract and a basal-lateral surface in contact with the blood. Currently, very little is known about endocrine regulation of colonic function. Receptors for insulin located on the basal-lateral membrane of the colon have recently been described by others, have now been able to isolate a preparation of colon epithelial cell mucosal brush border membranes containing little contamination with basal-lateral membranes and have shown that there are receptors for insulin in this unique membrane environment. Our purpose is to characterize the colon epithelial cell insulin receptors and to investigate the possible role of insulin in regulating the metabolic activity of this tissue. Insulin receptor characterization will include competition studies, insulin degradation, insulin receptor isolation following covalent cross-linking with 125I-insulin, specificity of insulin binding, binding studies with other hormones including IGF-I and IGF-II and receptor autophosphorylation. Possible areas of insulin action on the colon to be explored include the following: electrolyte absorption and secretion; water absorption; carbohydrate and amino acid uptake; glycolysis and glycogenesis; protein synthesis and the rate of cell growth. The methodology for achieving these goals has already been developed by the investigators who will participate in this project, but they have never focused on the colon before, due to the lack of evidence that any insulin receptors were present in this tissue. Our goal is to better understand the metabolism of mammalian colon epithelial cells and thereby to develop therapeutic approaches that will successfully intervene when a pathological condition such as colorectal cancer, diabetes mellitus or diarrhea leads to a change in colonic cell function.